1. Field of the Invention
The present invention relates to improved devices for supporting reinforcement rods within concrete so that the rods are held at selected levels above an earthen bed upon which the concrete is poured while the concrete sets up and hardens.
2. Description of the Prior Art
In pouring concrete to form roads, building slabs, sidewalks, bicycle paths and other slab-like structures on earthern beds, laterally extending reinforcement within the concrete is often required. Such reinforcement typically takes the form of a matrix of steel reinforcement "rebar" rods which are often tied together by wires to form a horizontally disposed, rectilinear grid. To properly reinforce a concrete slab it is extremely important for the reinforcement rods to be positioned at an appropriate elevation above the bed upon which the concrete is to be poured so that reinforcement is provided well within the structure of the concrete slab, and not merely on the lower face of the slab which resides in contact with the bed upon which the concrete is poured.
Supporting pedestals are provided to hold the reinforcement rods above the bed upon which the concrete is poured. The supporting pedestals are positioned at intervals which are spaced closely enough so that the reinforcement rods will not sag excessively between the supporting pedestals. Since the reinforcement rods are frequently quite heavy, it is often necessary to space the supporting pedestals every few inches in order to adequately support the reinforcement rods at the desired level above grade.
One very suitable type of pedestal for use in supporting reinforcement rods in concrete is constructed of molded high density plastic and is configured with a concave seat or cradle at its upper extremity, formed with a concave surface configured to receive and support conventional generally cylindrical steel reinforcing rods. The pedestal is provided with a plurality of uniformly spaced legs which diverge radially outwardly and downwardly at an inclination relative to the reinforcing rod seat. The pedestal legs terminate in feet which are spaced at uniform intervals radially outwardly from the center of the seat so as to provide the pedestal with some stability.
Reinforcing rod supporting pedestals of the type described are utilized both for supporting reinforcement rods above a solid, flat surface upon which concrete is to be poured, such as a wooden deck, and also to support reinforcement rods above a less stable foundation, such as an earthen bed of sand, gravel or soil. When reinforcement rod pedestals are placed upon a soft earthen bed, such as sand, the weight of the reinforcement rods causes the pedestal feet to dig into the sand or gravel. As a result, the pedestal is likely to tip and will not properly support the reinforcing rods at the desired elevation if placed directly upon an earthen bed.
To prevent the reinforcing rod pedestal from tipping, a flat bearing plate, known in the trade as a sand plate, is utilized to distribute weight from a pedestal located thereon. A conventional sand plate is a generally flat, disk-shaped structure which more uniformly distributes weight bearing downwardly through the pedestal legs and through the pedestal feet across a much greater surface area than the contact area of the pedestal feet. To ensure that the feet of the pedestal do not slip upon the sand plate, the sand plate is equipped with locating guides which are particularly adapted for use with a pedestal having feet of a particular size and located at specific distances of spatial separation from each other. Conventional sand plates and pedestals are thereby sold together as sets, and a particular model of sand plate is especially adapted for use with only a particular model of pedestal. Thus, in arranging for reinforcing rod supports a contractor or project engineer is forced to accurately coordinate the purchase of the proper quantity of sand plates for use with each different model of reinforcing rod pedestal purchased.